The Perfect Guitar
In the current state of the art, stringed instruments are basically fixed in shape, appearance and function at the time of manufacture or construction, with little or no ability to make radical or even substantive changes to those properties within the guitars themselves. At most, commonly available instruments can usually change appearance only by refinishing the surface or using appliques (U.S. Pat. No. 6,649,817) (or recutting the body, if solid), and change the quality of sound only by changing the strings and/or electronic pickups and circuits (if electric). It has been written that some blues players screwed soda bottle caps loosely to their acoustic guitars to create a harsher sound, which would horrify a classical guitarist. Electric guitarists commonly change their sound with exterior electronics, from mechanical reverberation to buzz boxes to digital audio processors. All [are] subject to the artist's taste, and artists may spend hundreds to thousands of dollars to find their perfect guitar, which often is reserved for just one of the styles of music and visual presentation the artist employs.
Pickups: Mounting and Adjustment
Note that the use of electric violins reportedly goes back to the 1920s (see http://en.wikipedia.org/wiki/Electric violin), and U.S. patents for electric violins go back to at least 1932 (see http://digitalviolin.com/Patents.html), for example U.S. Pat. No. 1,861,717, which included an electromagnetic bridge pickup and a skeletonized body. As early as the 1933 (U.S. Pat. No. 1,915,858), Miessner patented an electromagnetic pickup based upon a set of wire coils picking up the vibrations of strings near the static magnetic fields of a number of pole pieces. In 1936 (U.S. Pat. No. 2,026,841, Re20070), Lesti recognized that combining coils of opposite polarity would cancel out extraneous magnetic fields, later called humbucking, but used no permanent magnets in his pickup design. In 1948 (U.S. Pat. No. 2,455,575), Fender patented a pickup based upon the same physics as Meissner's, with a single coil. In 1951 (U.S. Pat. No. 2,557,754), Morrison patented a single-coil, six-pole guitar pickup little different from those seen on guitars today.
As early as 1961 (U.S. Pat. No. 2,976,755), Fender recognized that two single-coil pickups with permanent magnets of opposite magnetic polarity could be placed close together to cancel picking up exterior hum. Note that side-by-side coils in a humbucker produce a double-dipole field tends to reduce the reach of the field to the strings. Many other patents have followed but are incremental changes (Dave Hunter, The Guitar Pickup Handbook: The start of your sound, Backbeat Books, Milwaukee Wis., 2008; not a critical reference, since this patent does not cover a new type of pickup) to the three main types of electromagnetic pickup commonly sold today: the single-coil pickup, the humbucking pickup with two side-by-side coils, and the humbucking pickup with two stacked coils. The single-coil pickup tends to be the simplest, cheapest and easiest to produce, and can be made at home. Other pickups include piezoelectric, capacitive, light beam-interrupting LED and microphonic.
In most if not all electric guitars on the market today, including unfinished bodies for custom or home construction, have pickups placed in set positions, with at most two degrees of freedom in adjustment from those positions. The typical electromagnetic pickup can only be adjusted up and down at each end. Wright (U.S. Pat. No. 3,771,408, 1973), claims multiple mounting points for pickups, with three times as many pickup mounting holes as the usual electric guitar, but merely shows three separate pickups in FIG. 3, filling all the mounting holes, making no other claim of adjustability. Another (U.S. Pat. No. 4,254,683, 1981), allows up and down motion on just one axis, with horizontal motion between the neck and bridge.
Redard (U.S. Pat. No. 7,145,063 B2, 2006; U.S. Pat. No. 7,453,033 B2, 2008) has one of the most complicated pickup mounting and positioning systems, offering at most three degrees of freedom in positioning. Pickups in the system below the strings (2006) move in one degree of freedom between the bridge and neck, mounted on a set of parallel rods, with adjustment screws specified to adjust the distance between the strings and pickups. Both patents specify another pickup situated over the strings, rather inconveniently for anyone who wishes to pluck or strum them, moving on a track or bar parallel to the strings, rotating in angle across the strings with a vertical elevation adjustment above the strings, allowing three degrees of freedom in position. While horizontal angular rotation above the strings changes that orientation over the strings, it does not allow for alignment of the poles across the strings. It can be rotated away from string 1, the treble string, so that the pickup cannot appreciably detect string 1 vibrations, without any means to correct it.
U.S. Pat. No. 7,453,033 can claim four degrees of freedom, with adjustment screws at the ends of the pickup. In U.S. Pat. No. 7,145,063, FIGS. 8 and 9 show an apparent double-coil pickup, shown explicitly in U.S. Pat. No. 7,453,033, FIG. 3B, which is too far above the strings to reliably detect their vibrations, especially for the double-dipole field of that kind of pickup, which falls off faster with distance than a single-coil pickup.
Spalt (U.S. Pat. No. 7,060,888, 2006) has a single pickup that rotates horizontally about a fixed point under and beside the strings, allowing at most two degrees of freedom, if it also rotates slightly in the vertical, or can be adjusted vertically with washers on the pivot bolt.
Electric Stringed Instrument Bodies, Especially Guitars
In the area of body design, today's guitar market is dominated by acoustic guitars of standard design (some of which have electric pickups and amplifiers), electric guitars with solid bodies and electric guitars with hollow bodies with wall and soundboard construction which is considerably thicker and stiffer than acoustic instruments. Steel and resonator guitars might be considered a subtype of either acoustic or electric, depending upon amplification. Other non-acoustic stringed instruments, such as autoharps, and lap steel guitars comprise a small minority.
Some U.S. patents which address body improvements that either radically change the appearance of an instrument or allow an instrument's appearance to be radically changed fall into some general groups: skeletal or wire-frame bodies (U.S. Pat. Nos. 2,239,985, 3,413,883, 3,771,408); and modular bodies (U.S. Pat. Nos. 3,657,462, 4,254,683, 4,915,003, 5,637,823, 5,682,003, 5,929,362, 5,945,614, 6,046,392, 6,194,644, 6,525,246, 6,809,245, 6,911,590, 7,002,065, 7,141,730, and 7,442,865). Of the modular bodies, the large majority have a core section with the neck, strings, pickups (if any), bridge and tailpiece (if any), where the body attaches in one or more sections, with or without electronics.
One interesting variation (McGrew, U.S. Pat. No. 7,514,614, 2009) has a skeletonized body with an adjustable sound board, connected to the body of the guitar at only three points. However, the soundboard is constructed in several layers, including a single “large magnetic transducer”, impeding any vibration of the soundboard that could contribute to the sound of the instrument. The lever effect of McGrew's neck adjustments decree less effect on bridge tilt than vertical adjustments in line with the bridge. McGrew has no options for multiple sensors, adjustable in position.
Zoran (US-2010/0307313 A1, 2010; U.S. Pat. No. 8,217,254 B2, 2012) describe a semi-skeleton body with a soundboard top and electronics plugging into a central cavity. That soundboard has an electronic plug at the neck end and two points of suspension at the edges in line with the bridge, apparently held in place with string pressure. It has no vertical adjustments at the edges to counteract sag in the soundboard. Zoran describes sensors in the soundboard to pick up different modes of vibration. The soundboards of both McGrew and Zoran are limited in size and shape to the central body cavity. They cannot be further decorated or shaped or stressed to change the look of the entire guitar, or the major modes of vibration. Zoran's instrument in particular requires a level of manufacturing resources and expertise that precludes any major physical modifications by a kit builder in search of personal expression.
Electric Stringed Instrument Signal Amplification, Control and Modification
Although in this invention pickups may be mounted under the soundboard/top, through it without touching, or upon it, mounting pickups under it drives the need for an electronic pre-amplifier in the stringed instrument, as the detected string vibration signal will be smaller, due to the increased distance from standard pickups to the strings. Since many musicians who play electric stringed instruments also use external fuzz boxes, it makes sense to include such a feature in the preamp. In this regard, U.S. pat. No. 4,1800,707 (1979), U.S. Pat. No. 4,405,832 (1983), U.S. Pat. No. 4,995,084 (1991) and U.S. Pat. No. 7,787,634 (2010) seem to be the most relevant.
Moog's circuit produces “hard” and “soft” clipping to get third and higher order odd harmonics by overdriving a semiconductor transconductance amplifier, intending to replace vacuum tube circuits. It obtains even harmonics, intending to produce asymmetric waveforms, by using the same transconductance amplifier as a “squaring” element to generate “soft” even harmonics, and by a full-wave rectifier to generate “hard” even harmonics. Combinations of which could be mixed with the linear fundamental signal. Except for the more extremely asymmetrical signals with even harmonics, the linear fundamental predominated. The circuit largely maintained the character of the signal with automatic gain control, or AGC.
Sondermeyer's circuit is a simple diode clipper, which adds odd order harmonics, with a potentiometer output which varies continuously between the linear fundamental linear signal and the clipped signal, with some additional band-shaping. In simulation, Pritchard's analog distortion circuits produce various types of asymmetric clipping, with the linear fundamental signal tending to predominate over the harmonics.
U.S. Pat. No. 7,787,634 (Philip Young Dahl, 2010 Aug. 31) would seem to interfere the most with the electronic circuit presented here. The basic designs used both here and in Dahl's patent use concepts known in other fields, such as microwave and laser communications, as “analog predistorters”, which date back to at least the 1980s. For example, RF Examples.pdf, circa 2004, from http://cp.literature.agilent.com/litweb/pdf/ads2004a/dglin/dglin024.html, speaks of using anti-parallel diodes and biased diodes to generate Cubic Law and Square Law signals which are used for “eliminating the fundamental”.
Dahl's patent deals only with distortion emphasizing the third harmonic. It controls the ratio of the fundamental and third harmonic in the output primarily by changing the amplitude of the input signal before clipping by anti-parallel diode pairs. The remixing of the non-linear signal with the inverse of the linear signal to produce the third harmonic occurs only at a fixed gain. It does not then remix the third harmonic with the linear signal to produce a continuous range from the linear to the third harmonic to a predominately inverse linear signal after generation of the third harmonic. Nor does it attempt to generate any second harmonic signal.
Nor does it reduce the concept to its simplest terms using the simplest circuit, which can be demonstrated with an analog signal block diagram and associated equations, and which will predict the widest possible range of results, including emphasizing the second harmonic. It offers the puzzling term “non-limiting clipping”, which would seem to be a contradiction in terms.